﻿using System;
using System.Drawing;
using System.Runtime.InteropServices;
using Microsoft.Win32;

namespace Notoric.ViewModel.Internal
{
    /// <summary>
    /// Provides a function to get an icon that is registered with a specific file extension.<br/>
    /// The code was taken from this example
    /// http://stackoverflow.com/questions/616718/how-do-i-get-common-file-type-icons-in-c .
    /// </summary>
    internal static class Icons
    {
        /// <summary>
        ///     Creates an array of handles to large or small icons extracted from
        ///     the specified executable file, dynamic-link library (DLL), or icon
        ///     file. 
        /// </summary>
        /// <param name="lpszFile">
        ///     Name of an executable file, DLL, or icon file from which icons will
        ///     be extracted.
        /// </param>
        /// <param name="nIconIndex">
        ///     <para>
        ///         Specifies the zero-based index of the first icon to extract. For
        ///         example, if this value is zero, the function extracts the first
        ///         icon in the specified file.
        ///     </para>
        ///     <para>
        ///         If this value is �1 and <paramref name="phIconLarge"/> and
        ///         <paramref name="phIconSmall"/> are both NULL, the function returns
        ///         the total number of icons in the specified file. If the file is an
        ///         executable file or DLL, the return value is the number of
        ///         RT_GROUP_ICON resources. If the file is an .ico file, the return
        ///         value is 1. 
        ///     </para>
        ///     <para>
        ///         Windows 95/98/Me, Windows NT 4.0 and later: If this value is a 
        ///         negative number and either <paramref name="phIconLarge"/> or 
        ///         <paramref name="phIconSmall"/> is not NULL, the function begins by
        ///         extracting the icon whose resource identifier is equal to the
        ///         absolute value of <paramref name="nIconIndex"/>. For example, use -3
        ///         to extract the icon whose resource identifier is 3. 
        ///     </para>
        /// </param>
        /// <param name="phIconLarge">
        ///     An array of icon handles that receives handles to the large icons
        ///     extracted from the file. If this parameter is NULL, no large icons
        ///     are extracted from the file.
        /// </param>
        /// <param name="phIconSmall">
        ///     An array of icon handles that receives handles to the small icons
        ///     extracted from the file. If this parameter is NULL, no small icons
        ///     are extracted from the file. 
        /// </param>
        /// <param name="nIcons">
        ///     Specifies the number of icons to extract from the file. 
        /// </param>
        /// <returns>
        ///     If the <paramref name="nIconIndex"/> parameter is -1, the
        ///     <paramref name="phIconLarge"/> parameter is NULL, and the
        ///     <paramref name="phIconSmall"/> parameter is NULL, then the return
        ///     value is the number of icons contained in the specified file.
        ///     Otherwise, the return value is the number of icons successfully
        ///     extracted from the file. 
        /// </returns>
        [DllImport("Shell32", CharSet = CharSet.Auto)]
        extern static int ExtractIconEx(
            [MarshalAs(UnmanagedType.LPTStr)] 
        string lpszFile,
            int nIconIndex,
            IntPtr[] phIconLarge,
            IntPtr[] phIconSmall,
            int nIcons);

        /// <summary>
        /// Extracts an icon from a file extension.
        /// </summary>
        /// <param name="extension">Extension of the file</param>
        /// <param name="size">Desired icon size</param>
        /// <returns><see cref="Icon"/> instance if found or null otherwise</returns>
        public static Icon IconFromExtension(string extension, SystemIconSize size)
        {
            // Add the '.' to the extension if needed
            if (extension[0] != '.') extension = '.' + extension;

            //opens the registry for the wanted key.
            RegistryKey Root = Registry.ClassesRoot;
            RegistryKey ExtensionKey = Root.OpenSubKey(extension);
            ExtensionKey.GetValueNames();
            RegistryKey ApplicationKey =
                Root.OpenSubKey(ExtensionKey.GetValue("").ToString());

            //gets the name of the file that have the icon.
            string IconLocation =
                ApplicationKey.OpenSubKey("DefaultIcon").GetValue("").ToString();
            string[] IconPath = IconLocation.Split(',');

            if (IconPath[1] == null) IconPath[1] = "0";
            IntPtr[] Large = new IntPtr[1], Small = new IntPtr[1];

            //extracts the icon from the file.
            ExtractIconEx(IconPath[0],
                Convert.ToInt16(IconPath[1]), Large, Small, 1);
            return size == SystemIconSize.Large ?
                Icon.FromHandle(Large[0]) : Icon.FromHandle(Small[0]);
        }
    }

    /// <summary>
    /// Two constants extracted from the FileInfoFlags, the only that are
    /// meaningfull for the user of this class.
    /// </summary>
    internal enum SystemIconSize : int
    {
        Large = 0x000000000,
        Small = 0x000000001
    }
}
